Embodiments of the present invention relate to a high-speed electric motor of the integrated type, and more specifically to a high-speed motor compressor or turbo-compressor unit of the integrated type with a removable cartridge.
A high-speed motor is a motor whose rotation frequency is greater than the frequency of the electrical power network. A high-speed motor typically has a rotation speed of more than 3600 r.p.m.
A conventional integrated motor compressor unit is shown in part in FIG. 1. It comprises a sealed housing C in which are mounted an electric motor M and a compressor unit which is not shown, for example a multiple stage unit, which includes a plurality of compression impellers carried on an output shaft coupled to a rotor driven by the motor M.
The housing C, sealed by a cover T, has a first casing EC for containing the compressor, assembled together with a second casing EV in which the electric motor M is mounted. The electric motor M has a rotor R, a stator S, and first and second bearings P1 and P2 supporting the motor shaft, which are mounted, respectively, on a first and a second bearing support SP1 and SP2 positioned at either end of the rotor R.
The bearing supports SP1 and SP2 are mounted directly on the second casing EV. In this arrangement, the second support SP2 impedes access to the rotor R, and the first support SP1 can only be accessed by removing the first casing EC from the second casing EV.
The stator S of the motor M is shrink-fitted directly on to the motor casing EV, and therefore cannot be removed. The motor casing EV comprises a high-voltage wiring outlet O formed in a sealed way on a radial part of the housing C. This high-voltage outlet O is usually non-removable.
Removable cartridge systems are generally used by manufacturers of compressors and pumps. For example, in a compressor with a removable cartridge, the aerodynamic stator parts and the rotor are combined in a cartridge having a cylindrical outer shape which can be fitted into the main housing enabling the pressure to be adjusted. The bearings may be external to this cartridge or may be attached to the ends of the cartridge.
Various prior art documents relate to such arrangements.
U.S. Pat. No. 3,826,597 describes the use of a concept of this type in specific rotating machine applications such as vane-type compressors.
U.S. Pat. Nos. 5,971,702 and 4,961,260 describe principles of cartridge centring and insertion for centrifugal compressor applications.
With regard to the application of this concept to electrical machines, the U.S. Pat. Nos. 5,117,138 and 5,627,420 describe a removable electric motor stator. However, this patent is concerned with submersible pump applications. Furthermore, the removable stator is encapsulated in order to isolate it from the process gas, and the bearings are completely separated from this stator.
Finally, the U.S. Pat. No. 7,458,214 relates to a turbocharger application composed of a turbine wheel and a compressor wheel mounted in a projecting manner, and equipped with an auxiliary electric motor with a removable stator.
In the last three documents, the stator is not encapsulated, and in U.S. Pat. No. 7,458,214 the bearings are always separated from the stator.